It is known to form, for example, cups and lids from a thermoplastic film in a die assembly having a lower die formed with an array of pockets conforming to the outside surface of the workpieces to be made and an upper die that fits with the lower die and that has, in additional to optional plugs fittable into the pockets, nozzles that apply pressurized air to the top of the film above each pocket to deform it downward into the pockets. The two dies, which are normally heated to soften the film, are first moved vertically together to grip the film around each pocket and are pressed vertically together with considerable force while air is admitted and the film is deformed. Once the deformation is completed, the upper die is retracted upward and the lower die is tilted about a horizontal axis to hoop-cut the individual workpieces out of the film and discharge them from the press. The empty lower die is then returned to an upwardly open starting position, a new section of the film is advanced in a horizontal travel direction into position between it and the upper die, and another cycle can be started.
The relative vertical movement of the dies, or at least the vertical movement and tilting of the lower die (the terms “upper” and “lower” being purely relative and nonlimiting), is effected by an actuator or drive assembly comprising an electric motor, especially a servomotor, that is coupled by a transmission with the lower die. This drive motor has a flange coupled to a flange of the transmission, with a circular array of bolts or tie rods interconnecting the two flanges.
Such an actuators also has an intermediate coupling as an additional construction part, with an adapter bell between the electric motor and the transmission that houses the coupling and simultaneously is formed with the flange. In DE 91 08 344.3 an electric motor used as a drive configured with speed-reduction gears and a coupling on which the mold or swivel table of the lower die engages. As a rule, a servomotor is used, as is known from DE 40 33 534. It performs the pivoting by means of a crank motion or a spindle drive, while axial motion is done by means of a cam disk that is moved by a toggle linkage.
During the cutting out of the shaped workpieces from the film, strong impacts and vibrations occur in the actuator moving the dies toward each other. These act upon the drive system, primarily the electrical servomotor that actuates a cam-disk toggle linkage via a downstream transmission, at the end of which the mold table with the die that is mounted on it is mounted, and can cause damage to the motor parts, as well as to its control.